The symbol denoting a recycled product is simple and universal: three arrows in the shape of a triangle. So why isn't there an easy way to tell if a hotel is "green"? There is—in fact, there are far too many for any traveler to possibly keep track of them all.

More than 100 certification programs worldwide currently compete for travelers' attention. Dozens of countries have created their own certification systems, along with several American states. Other labels include those of industry groups (U.S. Green Building Council's LEED certification) or government agencies (the Environmental Protection Agency's Energy Star). And those are only the reputable ones.

To add to the confusion, there's no guarantee that a hotel with a stamp of approval is much better than one without any. Some programs don't audit their participants, relying instead on the honor code, a practice that Jorge Rivera, a professor of strategic management and public policy at Washington, D.C.'s George Washington University, says is actually one of the most prominent methods of greenwashing. In addition, many hotels that have high environmental standards never bother to get accredited.

That means you'll have to do some homework, as well as decide what's important to you. Travelers don't care about all environmental issues equally, and most don't want to think about them at all. But traveling sustainably means wanting to know—and being willing to ask.